It has heretofore been proposed for example as shown in U.S. Pat. Nos. 1,879,135, 3,132,773 and 3,396,102, to make a waste water treatment apparatus in which a carriage support rail extends across the top of the tank intermediate the side walls and a carriage is mounted on the rail and driven by a carriage drive including an endless chain that reciprocates the carriage along the rail and a tank cleaning head is connected to the carriage for movement thereby along a path adjacent the bottom of the tank. In the prior waste water treatment apparatus of this type, however, the chain drive and carriage were not enclosed so that the chain drive, carriage, and carriage support rail were exposed to the weather and it also presented a safety hazard to operating personel.
In order to simplify the controls and reduce the expense and power losses incident to use of a reversing motor drive to reciprocate the carriage, it has also been proposed, as disclosed in the aforementioned U.S. Pat. Nos. 1,879,135 and 3,132,773, to drive the endless chain in only one direction and to provide a connecting link connected at one end to the carriage and connected at its other end to the chain for reciprocating the carriage. However, the connecting link had to be offset from the plane of movement of the chain so that the reaction forces applied through the connecting link to the chain, which occur in driving the carriage, were laterally offset from the longitudinal centerline of the chain and tended to cause lateral loading of the chain with consequent uneven wear.